make prunning mode selectable: aggressive (cut off seen nodes in siblings and these children) or not (only cut off nodes from own walk path)
memoize results of make_requires_dict in rpmkit.rpmutils
add HTML and js templates to render rpm dependencies graph with using d3
add make_hierarchical_nested_dicts_from_paths() to dump paths gotten by walk in rpmkit.tree, and corresponding test cases